A car body of a rolling stock is formed by joining side structures and end structures (including a cab end structure) to four side portions of an underframe, then joining a roof structure to upper portions of the side structures and the end structures, and attaching outside plates, floor plates, interior decorative members, doors, windows, and the like to the structures. In addition, in the rolling stock, a passenger compartment is protected by reinforcing the end structures and the underframe portions or by providing impact absorbing members, as collision countermeasures.
Meanwhile, in recent rolling stocks, the car body width is increased by fully utilizing the rolling stock gauge. In many of such rolling stocks, since a lower portion of the car body comes close to a platform or the like, the car body width of the lower portion is set smaller than the upper portion of the car body. For this reason, the rolling stock having an increased car body width employs a so-called lower-side narrowed structure in which lower portions of the side structures are inclined to inner sides of the car body. In this structure, the lower end portions of side posts inclined to the inner sides of the car body do not intersect at right angles with side beams of the underframe in some cases, depending on the conditions of the rolling stock gauge, leading to a problem in the joint strength between the lower end portions of the side posts and the side beams.
As a joint structure between an underframe and side structures in a car body having such a lower-side narrowed structure as described above, one in which rocker rails joined to hem portions of side plates are joined to outer faces of side beams of the underframe is known (see for example Patent Document 1).